Compressors and more specifically centrifugal compressors, which are utilized as for example in providing the atomizing air to a spray painting system, have an inlet air supply. Atmospheric air enters an inlet plenum of a compressor and may be filtered by a relatively low pressure drop filter of the replaceable type. A filter is necessary to protect the internal parts of the compressor from damage due to dirt and particles that are present in the ambient air which may be drawn into the inlet plenum and compressor assembly.
The combination of a drive motor and a compressor where the motor drives the compressor is conventional. A conventional problem of excess heat is also created, the heat being generated by the motor and the drive mechanism between the motor and the compressor. Heat must be dissipated to the air to maintain the motor and compressor at proper operating temperatures. The compressed air will dissipate some heat from the compressor when it is operating efficiently. The heat dissipated from the machinery in general will heat and expand the air being delivered to the inlet of the compressor. This is a problem because a centrifugal compressor is inherently a constant mass machine. Thus, the greater the inlet air temperature, the greater the outlet pressure of the air of a given mass. This is a problem to be solved, namely, how to dissipate the heat while minimizing the volume of heated air delivered to the compressor inlet.
Another problem is the heat generated within the compressor during normal operations. In a spray painting system, the spray guns do not operate all the time or at a constant volume. For various reasons, the operator (be it automatic or manual) activates the spray gun for a period of time and then deactivates it as needed for the ongoing operation. A plurality of spray guns supplied from a manifold create an oscillating need for air which is inconsistent with the output from a constant output air compressor. As a result of the oscillating usage of air, there is a heat buildup in the compressor which not only inceases wear on parts, but also makes the mass output to vary and the air temperature to oscillate. Spray guns are designed to operate satisfactorily over a range of temperatures, but changing the air temperature will inherently change the spray characteristics of the paint being dispensed. Thus, there is a need to control the temperature of air in a spray painting system.
Air compressors are designed with an exterior surface to dissipate heat and at an air dispensing rate which will keep the compressor parts at a temperature within acceptable ranges. When the pressure differential from inlet to outlet is too great, the compressor temperature increases. When the back pressure at the outlet increases due to reduced usage by the spray guns, the temperature of the compressor increases for two reasons, (1) the motor has to work harder to push the air out of the housing and (2) less air passes through the compressor and thus must absorb more heat per unit of air.